Experiments will be done with isolated rat pancreatic islets to test whether hydrogen shuttles are involved in supporting insulin secretion and to attempt to identify which shuttles are involved. There is considerable evidence that the stimulus for glucose-induced insulin release involves glucose metabolism. During glycolysis reducing equivalents (NADH) will be formed in the cytosol of the beta cell. Unless the NADPH is reoxidized, the cytosolic NAD/NADH ratio will decrease and since NAD is required for the step in glycolysis catalyzed by glyceraldehyde phosphate dihydrogenase, glucose metabolism will be diminished. The most efficient means for re-oxidizing cytosolic reducing equivalents is by hydrogen shuttles which transfer reducing equivalents to the mitochondrial electron transport chain. Preliminary studies showed: 1) High concentrations of inhibitors of the malate-aspartate shuttle (aminooxyacetate and butylmalonate) and of the malate-oxaloacetate shuttle do not interfere with glucose-induced insulin release or CO2 production from glucose. 2) The content of mitochondrial glycerol 3-phosphate dehydrogenase, an enzyme known to function only in the glycerol 3-phosphate shuttle, was found to be 30-60 times higher in pancreatic islets than in liver, pancreatic acinar tissue, heart or skeletal muscle. 3) Diazoxide, a well-known inhibitor of insulin release in vivo and in vitro, inhibited the assayable activity of the mitochondrial glycerol 3-phosphate dehydrogenase. Studies of insulin release, metabolite flux, activities of enzymes possibly involved in shuttles, will be done and studies with pancreatic islet mitochondria will be attempted.